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ORCA – Oscillation Research with Cosmics in the Abyss

Scheme of the two neutrino mass hierarchies.

With the ORCA (Oscillation Research with Cosmics in the Abyss) detector the KM3NeT collaboration will study a fundamental question of particle physics: that of the relative ordering of the neutrino masses, also referred to as the neutrino mass hierarchy – i.e. the question whether the third neutrino mass eigenstate is heavier (normal hierarchy) or lighter (inverted hierarchy) than the first and second states. The influence of the mass hierarchy on neutrino oscillations in matter leaves its imprint on the atmospheric neutrino flux via the characteristic appearance/disappearance patterns of the different neutrino flavours as a function of energy and path through the Earth.

The ORCA detector will be deployed about 40 km off-shore Toulon, France. A multi-megaton scale array of KM3NeT light sensor modules will be used for studying reactions of atmospheric neutrinos with the seawater. In its dense configuration, the detector is capable to detect neutrinos with energies as low as about one GeV, which is three orders of magnitude lower that the typical energy scale probed by the ARCA telescope for neutrino astroparticle physics.

The first construction phase of ORCA has started and forsees in a prototype array comprising 7 vertical detection units. This prototype array is expected to be concluded and operational in summer 2019. The full ORCA detector will comprise 115 detection units instrumenting a volume of about 6 Mton of sea water and could be operational towards 2020.

For more information, please refer to the KM3NeT Homepage.